Folded path acoustic delay line and optical processor

ABSTRACT

A folded path acoustic device of a homogeneous solid material in which an acoustic signal is folded in a non-overlapping path used as a processor or delay line. The acoustic signal is reflected from facets of the body in a planar path in a manner to avoid mode conversion. The acoustic signal can also be folded from one planar path to another in a three-dimensional configuration of the delay line.

United Stat Gottlieb et al.

[ 1 FOLDED PATH ACOUSTIC DELAY LINE AND OPTICAL PROCESSOR Inventors:Milton Gottlieb, Pittsburgh; John J.

Conroy, Verona, both of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Apr. 20, 1972 Appl. No.1 246,007

U.S. Cl. 333/30 R, 350/161 Int. Cl H03h 7/30, G02f 1/28 Field ofSearch...333/30 R; 310/8, 8.1; 350/161 [56] References Cited UNITEDSTATES PATENTS 10/1969 Stelting 333/30 R X 1/1967 Polucci 333/30 R2/1957 Geoghegan 333/30 R 4/1950 McSkimin 1 3l0/8.1

Skaggs 333/30 R 1 1 Feb. 26, 1974 3,680,008 7/1972 Yamamoto 333/30 R3,522,557 8/1970 Duncan et al 333/30 R FOREIGN PATENTS OR APPLICATIONS1,255,214 11/1967 Germany 333/30 R 823,846 11/1959 Great Britain 333/30R Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin NussbaumAttorney, Agent, or FirmC. L. ORourke [57] ABSTRACT A folded pathacoustic device of a homogeneous solid material in which an acousticsignal is folded in a nonoverlapping path used as a processor or delayline. The acoustic signal is reflected from facets of the body in aplanar path in a manner to avoid mode conversion. The acoustic signalcan also be folded from one planar path to another in athree-dimensional configuration of the delay line.

16 Claims, 5 Drawing Figures OR IN- 333/3012 FOLDED PATH ACOUSTIC DELAYLINE AND OPTICAL PROCESSOR BACKGROUND OF THE INVENTION 1. Field of theInvention v This invention relates'to solid ultrasonic delay lines ingeneral. More particularly, it applies to optoacoustic processorswherein it is necessary to process signals of long duration in anoptical system.

2. Description of The Prior Art It has been the general practice toconstruct multifacet delay lines using essentially a polygonal shapeddevice. Usually the signal is introduced by means of a transducer andundergoes a series of reflections from the multiple sides of the delayline until finally it is extracted from the delay line by a secondtransducer or absorbed by some absorption medium. However, segments ofthe path of the acoustic signal in such a device generally overlap withother segments. Such overlap may introduce interference between thesesegments that is not tolerable in an opto-a'coustic system.

Another type of delay line extended the single layer polygonal disc intoa three dimensional structure. This type of structure allows longersignals to be stored or processed. However, some aberration isintroduced in the process of transferring the signal of one layer to thenext layer of the polygonal delay line. For an example of this type ofdevice, see U.S. Pat. No. 3,025,479 issued to John M. Wolfskill.

Another type of delay line which allows for differential delay in thetransmission time is disclosed in U.S. Pat. No. 3,227,970 issued toWalter M. Andersen. An dersen shows a delay line in which a movablemember which includes refracting surfaces is mounted on top of the delayline. Such a delay line, however, is not made of one integral solidpiece, but requires precise mounting of the movable member and alsoprecise alignment so that the signal is properly transmitted through thedelay line. Neither can Andersens teaching be extended to encompass athree-dimensionally folded delay line. Further, the laminated typeconstruction of the Andersen device has the potential for introducingdiscontinuities which are not tolerable in an optoacoustic system.

Another delay line using a liquid medium for transmission of compressionwaves is disclosed in U.S. Pat. No. 2,505,364 issued to H. J. McSkimin.McSkimin shows a system wherein the compression waves are transmittedthrough a series of parallel branches containing liquid mercury, foldedfrom one to the next adjacent branch by a series of reflections fromsurfaces set at 45 to the direction of propagation. However, in such aliquid system distortion is difficult to control, i.e., mode conversionis a problem even though not introduced necessarily by the reflectionsthe wave undergoes. Such a system could not be used in an optical systemsince it is not transparent to light and further is not conductive toconduction of shear waves.

SUMMARY OF THE INVENTION The subject invention is directed to anacoustic delay line or processor for processing and transmittingacoustic signals preferably in an opto-acoustic system and comprises asolid integral body of acoustic signal conducting material whichincludes at least one planar path for carrying the acoustic signal in afolded nonoverlapping path, an input transducer connected to theintegral body and an absorber connected to the solid integral body toprevent reflection of the signal back into the line. The folded path isaccomplished without mode conversion by a selective choice of alignmentangles of the reflective facets includes in the body of the delay line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a projection view of anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION In order to understand theoperational environment of the subject invention, it is helpful to referto the block diagram shown in FIG. 1a, wherein reference numeral 2represents the folded path acoustic device which is the subject of thepresent invention, being utilized in an opto-acoustic system forprocessing of acoustic signals. The block diagram shown in FIG. l'b,wherein reference numeral 12 represents a folded path acoustic devicewhich is a second embodiment of the present invention, is anotheropto-acoustic system in which the subject invention can be used.

Referring to FIG. 1a, a laser beam 3 is incident normally (or at theBragg angle) upon the face of acoustic delay line 2. An RF. signal isinjected at transducer 4 to the delay line 2 and, as will be pointed outin greater detail, the signal is folded in a path perpendicular to theincident laser beam. This opto-acoustic device relies on the phenomenaassociated with the Debye-Sears effect or with the Bragg effect fordiffraction of light; that is, that a collimated laser beam isdiffracted by an acoustic signal of carrier frequency f into an angle(15 Af/v, while the frequency of the diffracted light is shifted fromthat of the original beam by the amount of the acoustic frequency. Inthe above expression the light wavelength is It, the acoustic velocityis v, and the frequency of the acoustic signal is f. In the simplesystems as shown in FIGS. la and 1b, the diffracted light intensity isdirectly detected by a photo-detector 10 after passing through lens 8.The photo-detector 10, located in the Fourier transform plane orphoto-detection plane, is connected to appropriate processing circuitryfor processing of the information obtained from the acoustic signal.Such circuitry does not form any part of the subject invention.

FIG. 1a utilizes acoustic device 2 which has mounted thereon transducer6 for injection of a reference signal to be compared to the RF signalwhich is injected to the acoustic device 2 by transducer 4. The systemof FIG. 1b obtains similar results but instead of a reference signalbeing introduced into the acoustic device 12, a transparency 18containing the spatial frequency of an acoustic wave is placed paralleland adjacent to the delay line.

The opto-acoustic device 20 shown in FIG. 2 represents one embodiment ofthe subject invention constructed from a solid integral piece ofacoustic signal conducting material such as fused quartz in. which theacoustic wave is transmitted in a two dimensional path. This correlatoror processor takes advantage of the principle that no mode conversiontakes place for a shear wave incident at 45 to a reflecting surface,with the shear polarization in the plane of incidence. This principle iswell known in the art as discussed by R. N. Thurston in PhysicalAcoustics, W. P. Mason, Editor (Academic Press, New York, 1964) VolumeI, pages 8 l-84. Thus, the shear wave transmitted through acoustic delayline is reflected at each and every facet so that the angle of incidenceis always 45, thereby preventing mode conversion. This shearpolarization direction is also that for which light incident normal tothe plane of the delay line is most efficiently diffracted.

The opto-acoustic correlator or processor shown in FIG. 2 includestransducers 22 and 24 for injecting an RF signal and a replica signalrespectively into device 20. Absorbers and 23 prevent the reflection ofthe respective signals back into the device 20. It will be understoodfrom the discussion above of FIG. 1b that transducer 24 and absorber 23can be eliminated for certain applications. The absorber 25 can also beeliminated if reflection of the acoustic wave back into theopto-acoustic device 20 is not critical to the particular signalprocessing application. If the device 20 is used as a delay line, anoutput transducer would replace absorber 25.

The device 20 shown in FIG. 2 has parallel planar surfaces 29 and 27.Reflective side surfaces 31 and 33 are oppositely displaced from oneanother and have serrations formed thereon characterized by peaks andvalleys parallel to the planar surfaces 29 and 27.

Looking now at FIG. 3 a more detailed description of the opto-acousticdevice 20 is given below. An RF signal is introduced to delay line 20 bymeans of transducer 22. The signal follows a planar path 26. The signalis initially reflected from facet 28-1 which is inclined 45 to the pathof the signal. The signal undergoes a second reflection at facet 28-2which also is inclined at 45 to the direction of propagation of thesignal. The double reflection of the signal from facets 28-1 and 28-2causes the signal to reverse direction by 180 following branch 32-2. Thesignal in effect is folded from branch 32-1 to branch 32-2 by means ofreflecting surfaces 28-1 and 28-2. Branches 32-1 and 32-2 are paralleland coplanar. This folding action is repeated at facet -1 and 30-2,causing the signal to fold back to branch 32-3 which parallels branches32-1 and 32-2. The shear wave will continue to taverse the path 26 ofdelay line 20 along a multiplicity of parallel branches 32-1, 32-2, etc.being folded at facets 28-1 and 28-2, 30-1 and 30-2, 28-3 and 28-4, etc.

The segments of the path 26 which are vertical to the longitudinalbranches 32-1, 32-2, 32-3, etc. identified by symbols 34-1 and 34-2typically account for about 6 percent of the total path of the signal.Because of the vertical segments of the path, when the device is used inan opto-acoustic system, photo-detectors in the focal plane must providefor diffraction in both the horizontal and vertical directions, unlessthe vertical segments of the signal may be discarded.

A replica or reference signal can be introduced at transducer 24 andtransmitted through delay line 20 along a folded path 36, as shown inFIG. 3. Planar path 36 is identical to planar path 26 except fortraversing the delay line 20 in the opposite direction. Path 36 can beparallel and spaced apart from path 26 as shown in FIG. 2, or it can becoextensive with path 26 and not spaced apart. Such oppositely movingacoustic signals produce a correlation signal which, for example, can beacted upon by an incident laser beam.

An opto-acoustic correlator or delay line as shown in FIG. 2 could, forinstance, have a total acoustic path length of about 82 centimeters whenfabricated from an initial blank 7.6 centimeters square. Such a designwhich folds the acoustic wave into substantially a square format allowsthe device to be incorporated in an opto-acoustic system using roundrather than cylindrical optics, and thereby requiring a much smalleraperture for processing the same amount of information than if theacoustic path length had not been folded. In this type of opto-acousticcorrelator only shear waves polarized in the plane of incidence may beused to avoid mode conversion upon reflection and to provide for highlight diffraction efficiency.

The folded path acoustic delay line shown in FIG. 2 can be extended intothree dimensions. The extension into three dimensions is achieved bynoting that the condition of no mode conversion upon reflection may alsobe satisfied for a configuration of incidence in which the shearpolarization direction is parallel to the surface. These conditions aresatisfied by the folded path acoustic delay line shown in FIG. 4. Thedevice of FIG. 4 has parallel planar surfaces 51 and 53. Side surfaces55 and 59 are oppositely displaced one from another and each surface hastwo sets of serrations. Looking at side surface 55 it is seen that oneset of serrations is characterized by reflective facets 56-1 to 56-6 andthe second set of serrations is characterized by reflecting surfaces62-1 to 62-8. The peaks and valleys defined by reflective facets 56-1 to56-6 lie parallel to the planar surfaces 51 and 53. The peaks andvalleys defined by reflective surfaces 62-1 to 62-8 lie normal to theplanar surfaces 51 and 53.

The input signal is projected into the delay line 50 by means of inputtransducer 52. The shear wave follows folded path 54. It is reflectedfrom facets 56-1 through 56-6 and 57-1 through 57-6 of the delay line50, each of which is inclined 45 to the direction of propagation of theacoustic signal. The shear wave follows the path 54 which is comprisedof a series of parallel branches 58-1 through 58-7 and segments 60-1through 60-6 which are perpendicular to branches 58-1 through 58-7. Theshear wave traverses the folded path 54 with its polarization in theplane of incidence, and incident at 45 to the reflecting surfaces at alltimes. After the shear wave traversesthe last branch 58-7 of the planarpath 54, the shear wave undergoes two reflections with polarizationparallel to the reflecting surfaces 62-1 and 62-2. In this manner theshear wave is folded into a second planar path parallel to the first.This process may be repeated for as many planar paths as are provided inthe particular delay line. An obvious result of this method of foldingthe acoustic wave is that no branch in the path overlaps any otherbranch. Since the branches of the path do not overlap, intra signalinterference is avoided. A second transducer 64 may be used either toextract the acoustic signal from the delay line, or to project a replicain when using the device as an opto-acoustic correlator.

It should be understood that the parallel branches of each planar pathas shown in FIG. 4 can be increased by utilizing a larger piece ofacoustic signal conducting material having a corresponding larger numberof refleeting facets 56. The number of parallel planar paths also may beincreased by utilizing a piece of acoustic signal conducting materialhaving a larger number of reflecting surfaces 62, the number beinglimited only by possible interference between adjacent branches whenspaced too closely together.

A typical relationship between the length of the parallel branches 58and the segments 60 which are perpendicular to branches 58 is to 1.Thus, in such a configuration, approximately 10 percent of the totalpath is vertical to the major part of the path. However, this dimensioncan obviously be varied depending upon the application and theparticular type of optical processing involved.

This opto-acoustic device allows for the folding of the path of anacoustic signal in three dimensions which is free of mode conversion forall reflections. The manner in which the acoustic path is folded inthree dimensions is particularly suitable for opto-acoustic signalprocessing because each branch is isolated from all other branches. Forsuch signal processing, the device of our invention might morespecifically be described as an opto-acoustic correlator or processor.It is therefore to be understood that the terms correlator or processoralong with delay line are within the meaning of the opto-acoustic devicedescribed in this specification.

What is claimed is:

1. A folded path acoustic device for processing acoustic wave signals,comprising:

a homogeneous solid integral body of acoustic signal conductingmaterial, said body having a planar path for conducting said acousticwave signal including a plurality of parallel branches terminated byreflective facets adapted to fold said acoustic wave signal from one ofsaid branches to the next adjacent of said branches so that said signalremains in phase from branch to branch in a non-overlapping path, and

first transducer means connected in a signal transferral relationshipwith said body for input of said acoustic wave signal into a selectedbranch of said acoustic device.

2. The acoustic device as set forth in claim 1 wherein said devicefurther includes means connected in a signal transferral relationshipwith said body for receiving said acoustic signal.

3. The acoustic device as set forth in claim 2 wherein said meansincludes an absorber adapted to prevent reflection of said acoustic wavesignal back into said acoustic device.

4. The acoustic device as set forth in claim 2 wherein said meansincludes an output transducer whereby said device can be used as anacoustic delay line.

5. The acoustic device as set forth in claim 1 wherein said transducermeans is a shear-wave transducer connected to a selected one of saidbranches of said planar path adapted to polarize said acoustic wavesignal in the plane of incidence of said acoustic wave with saidreflective facets of said selected branch.

6. The acoustic device as set forth in claim 5 wherein said reflectivefacets are aligned at 45 to the direction of propagation of saidacoustic signal.

7. The acoustic device as set forth in claim 6 wherein said homogeneoussolid body includes said planar path having a number of said parallelbranches such that said planar path assumes substantially a squareformat in the plane of said planar path whereby round optics can be usedto process optical signals transmitted through said solid body by meansof said acoustic signal.

8. The acoustic device as set forth in claim 6 which further includes asecond planar path for conducting a replica acoustic signal having aplurality of parallel branches and second transducer means connected ina signal transferral relationship with a selected one of said branchesof said second planar path for input of said replica acoustic signal tosaid selected branch of said second planar path.

9. The acoustic device as set forth in claim 8 wherein said secondplanar path is coextensive with said first planar path.

10. A folded path acoustic device for processing an acoustic wave signalcomprising:

a homogeneous solid integral body of acoustic signal conductingmaterial;

first transducer means connected in a signal transferral relationshipwith said body for input of said acoustic wave signal to said acousticdevice;

said body having a plurality of parallel planar paths for carrying saidacoustic wave signal, each of said planar paths including a plurality ofparallel branches terminating in reflective facets adapted to foldwithout mode conversion said acoustic wave signal from one of saidbranches to the next adjacent of said branches so that said acousticwave signal is passed in a non-overlapping path in phase from branch tobranch,

said planar paths further including reflective means adapted to foldsaid acoustic wave signal from one of said planar paths to a nextadjacent one of said planar paths whereby said acoustic wave signal ispassed in a non-overlapping path from planar path to planar path; and

means connected in a signal transferral relationship with said body suchthat said acoustic wave signal is not reflected back into said delayline.

11. The acoustic device as set forth in claim 10 wherein said meansinclude an absorber adapted to prevent reflection of said acoustic wavesignal back into said acoustic device.

12. The acoustic device as set forth in claim 10 wherein said meansinclude an output transducer whereby said device can be used as anacoustic delay line.

13. The acoustic device as set forth in claim 10 wherein said firsttransducer means is a shear-wave transducer adapted to polarize saidacoustic signal in a plane of incidence of said acoustic wave signalwith said reflective facets of said branches.

14. The acoustic device as set forth in claim 13 wherein said reflectivefacets are at 45 to the direction of propagation of said acoustic wavesignal.

15. The acoustic device as set forth in claim 14 wherein said reflectivemeans includes two reflective surfaces at to each other and 45 to thedirection of propagation of said acoustic wave signal for folding saidacoustic signal from one planar path to a next adjacent planar pathwhereby said acoustic signal does not undergo mode conversion.

and valleys so arranged and constructed that said peaks and valleys areparallel to said first and second planar surfaces and a second set ofserrations having peaks and valleys so arranged and constructed thatsaid peaks and valleys are normal to said first and second planarsurfaces.

1. A folded path acoustic device for processing acoustic wave signals,comprising: a homogeneous solid integral body of acoustic signalconducting material, said body having a planar path for conducting saidacoustic wave signal including a plurality of parallel branchesterminated by reflective facets adapted to fold said acoustic wavesignal from one of said branches to the next adjacent of said branchesso that said signal remains in phase from branch to branch in anon-overlapping path, and first transducer means connected in a signaltransferral relationship with said body for input of said acoustic wavesignal into a selected branch of said acoustic device.
 2. The acousticdevice as set forth in claim 1 wherein said device further includesmeans connected in a signal transferral relationship with said body forreceiving said acoustic signal.
 3. The acoustic device as set forth inclaim 2 wherein said means includes an absorber adapted to preventreflection of said acoustic wave signal back into said acoustic device.4. The acoustic device as set forth in claim 2 wherein said meansincludes an output transducer whereby said device can be used as anacoustic delay line.
 5. The acoustic device as set forth in claim 1wherein said transducer means is a shear-wave transducer connected to aselected one of said branches of said planar path adapted to polarizesaid acoustic wave signal in the plane of incidence of said acousticwave with said reflective facets of said selected branch.
 6. Theacoustic device as set forth in claim 5 wherein said reflective facetsare aligned at 45* to the direction of propagation of said acousticsignal.
 7. The acoustic device as set forth in claim 6 wherein saidhomogeneous solid body includes said planar path having a number of saidparallel branches such that said planar path assumes substantially asquare format in the plane of said planar path whereby round optics canbe used to process optical signals transmitted through said solid bodyby means of said acoustic signal.
 8. The acoustic device as set forth inclaim 6 which further includes a second planar path for conducting areplica acoustic signal having a plurality of parallel branches andsecond transducer means connected in a signal transferral relationshipwith a selected one of said branches of said second planar path forinput of said replica acoustic signal to said selected branch of saidsecond planar path.
 9. The acoustic device as set forth in claim 8wherein said second planar path is coextensive with said first planarpath.
 10. A folded path acoustic device for processing an acoustic wavesignal comprising: a homogeneous solid integral body of acoustic signalconducting material; first transducer means connected in a signaltransferral relationship with said body for input of said acoustic wavesignal to said acoustic device; said body having a plurality of parallelplanar paths for carrying said acoustic wave signal, each of said planarpaths including a plurality of parallel branches terminating inreflective facets adapted to fold without mode conversion said acousticwave signal from one of said branches to the next adjacent of saidbranches so that said acoustic wave signal is passed in anon-overlapping path in phase from branch to branch, said planar pathsfurther including reflective means adapted to fold said acoustic wavesignal from one of said planar paths to a next adjacent one of saidplanar paths whereby said acoustic wave signal is passed in anon-overlapping path from planar path to planar path; and meansconnected in a signal transferral relationship with said body such thatsaid acoustic wave signal is not reflected back into said delay line.11. The acoustic device as set forth in claim 10 wherein said meansinclude an absorber adapted to prevent reflection of said acoustic wavesignal back into said acoustic device.
 12. The acoustic device as setforth in claim 10 wherein said means include an output transducerwhereby said device can be used as an acoustic delay line.
 13. Theacoustic device as set forth in claim 10 wherein said first transducermeans is a shear-wave transducer adapted to polarize said acousticsignal in a plane of incidence of said acoustic wave signal with saidreflective facets of said branches.
 14. The acoustic device as set forthin claim 13 wherein said reflective facets are at 45* to the directionof propagation of said acoustic wave signal.
 15. The acoustic device asset forth in claim 14 wherein said reflective means includes tworeflective surfaces at 90* to each other and 45* to the direction ofpropagation of said acoustic wave signal for folding said acousticsignal from one planar path to a next adjacent planar path whereby saidacoustic signal does not undergo mode conversion.
 16. A homogeneoussolid integral body of acoustic signal conducting material comprising: afirst planar surface, a second planar surface parallel to and spacedapart from said first planar surface, first and second oppositelydisplaced side surfaces each having a first set of serrations havingpeaks and valleys so arranged and constructed that said peaks andvalleys are parallel to said first and second planar surfaces and asecond set of serrations having peaks and valleys so arranged andconstructed that said peaks and valleys are normal to said first andsecond planar surfaces.